This invention relates to a tilting device for a marine propulsion unit and more particularly to an improved hydraulically operated tilting device including an improved pressure relief and bypass valve for such devices.
As is well known, a wide variety of hydraulic systems have been employed for achieving tilt and trim movement of a marine outboard drive. With these types of devices, a hydraulic motor, normally of the reciprocating type is interposed between the transom of the watercraft and the outboard drive for adjusting the trim of the outboard drive in response to extension and contraction of the fluid motor. The fluid motor is powered by a fluid system that is contained, normally, within the hull of the watercraft and which may, at times, include a reversible electric driving motor and a reversible fluid pump. In connection with such systems, it is the normal practice to provide pressure relief valves in the circuitry to the fluid motor so as to relieve the pressure in the event an impact is encountered and protect the system from damage. Normally, such arrangements use two relief valves, one in communciation with each chamber of the fluid motor so as to absorb impacts in either direction. Of course, the use of such circuits employing two valves, one for each direction of movement, adds to the complexity of the system and thus can increase the cost and may, in fact, reduce the reliability of the system.
It is, therefore, a principal object of this invention to provide an improved tilting device for a marine propulsion unit.
It is another object of this invention to provide an improved pressure relief system for a hydraulic tilting device for a marine propulsion unit.
In addition to the pressure relief functions aforedescribed, frequently, hydraulic tilt and trim systems employ some form of manually operable bypass valve for permitting manual movement of the outboard drive without interference from the hydraulic motor that operates the tilt and trim unit. The manual relief valve must provide, in addition to a free source of fluid between the two chambers of the fluid motor, some arrangement for insuring makeup fluid can flow from the reservoir into the system so as to compensate for the change of area affected in one of the chambers by the varying displacement of the piston rod therein. Therefore, valves proposed for this purpose have been somewhat complicated and, furthermore, have required the use of separate tools to open and close the valve. The use of such a separate tool obvious presents certain difficulties.
It is, therefore, a further object of this invention to provide an improved manually operable bypass valve for a hydraulic tilt and trim unit of a marine outboard drive.